The present invention relates to a class of hydrochlorofluorocarbons which have 3 to 5 carbon atoms, have 1 to 2 chlorine atoms, and have OH rate constants from about 8 to about 25 cm.sup.3 /molecule/sec.times.10-14.
Vapor degreasing and solvent cleaning with fluorocarbon based solvents have found widespread use in industry for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.
In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room-temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves behind no residue as would be the case where the object is simply washed in liquid solvent.
For soils which are difficult to remove, where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently and quickly, the conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing.
Vapor degreasers suitable in the above-described operations are well known in the art. For example, Sherliker et al. in U.S. Pat. No. 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump, a water separator, and other ancilliary equipment.
Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications, the soiled part is either immersed in the fluid or wiped with rags or similar objects soaked in solvents.
In cold cleaning applications, the use of the aerosol packaging concept has long been found to be a convenient and cost effective means of dispensing solvents. Aerosol products utilize a propellant gas or mixture of propellant gases, preferably in a liquefied gas rather than a compressed gas state, to generate sufficient pressure to expel the active ingredients, i.e. product concentrates such as solvents, from the container upon opening of the aerosol valve. The propellants may be in direct contact with the solvent, as in most conventional aerosol systems, or may be isolated from the solvent, as in barrier-type aerosol systems.
Chlorofluorocarbon solvents, such as trichlorotrifluoroethane, have attained widespread use in recent years as effective, nontoxic, and nonflammable agents useful in degreasing applications and other solvent cleaning applications. Trichlorotrifluoroethane has been found to have satisfactory solvent power for greases, oils, waxes and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts, printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts and the like. Trichlorotrifluoroethane has two isomers: 1,1,2-trichloro-1,2,2-trifluoroethane (known in the art as CFC-113) and 1,1,1-trichloro-2,2,2-trifluoroethane (known in the art as CFC-113a). CFC-113 has a boiling point of about 470.degree. C. and has been found to have satisfactory solvent power for greases, oils, waxes, and the like.
Another commonly used solvent is chloroform (known in the art as HCC-20) which has a boiling point of about 630.degree. C. Perchloroethylene is a commonly used dry cleaning and vapor degreasing solvent which has a boiling point of about 121.degree. C. These compounds are disadvantageous for use as solvents because they are toxic; also, chloroform causes liver damage when inhaled in excess.
Although chlorine is known to contribute to the solvency capability of a compound, fully halogenated chlorofluorocarbons and hydrochlorofluorocarbons are suspected of causing environmental problems in connection with the earth's protective ozone layer. Thus, the art is seeking new compounds which do not contribute to environmental problems but yet provide the solvency properties of CFC-113.
Chlorofluorocarbons (CFCS) such as CFC-113 are suspected of causing environmental problems in connection with the ozone layer. Under the Clean Air Act, CFC-113 is being phased-out of production.
In response to the need for stratospherically safe materials, substitutes have been developed and continue to be developed. Research Disclosure 14623 (June 1978) reports that 1,1-dichloro-2,2,2-trifluoroethane (known in the art as HCFC-123) is a useful solvent for degreasing and defluxing substrates. In the EPA "Findings of the Chlorofluorocarbon Chemical Substitutes International Committee", EPA-600/9-88-009 (April 1988), it was reported that HCFC-123 and 1,1-dichloro-1-fluoroethane (known in the art as HCFC-141b) have potential as replacements for CFC-113 as cleaning agents.
The problem with these substitutes is that they have a long atmospheric lifetime as determined by their reaction with OH radicals in the troposphere. Table I below contains the OH rate constants and corresponding atmospheric lifetimes for these substitutes. In Table I, Exp K.sub.OH stands for experimental K.sub.OH rate constant, Est K.sub.OH stands for estimated K.sub.OH rate constant, Exp Life stands for experimental lifetime, and Est Life stands for estimated lifetime. The unit on the rate constant is cm.sup.3 /molecule/sec.times.10-14 and the unit on the lifetime is years.
TABLE I ______________________________________ Exp Est Exp Est Number Formula K.sub.OH K.sub.OH Life Life ______________________________________ HCFC-123 CHCl.sub.2 CF.sub.3 3.7 2.96 2.0 2.6 HCFC-124 CF.sub.3 CHClF 1.0 1.00 7.5 7.5 HCFC-141b CFCl.sub.2 CH.sub.3 0.75 2.10 10.1 3.6 HCFC-142b CF.sub.2 ClCH.sub.3 0.38 2.10 19.9 6 HCFC-225ca CF.sub.3 CF.sub.2 CHCl.sub.2 2.49 3.30 2.3 2.3 HCFC-225cb CClF.sub.2 CF.sub.2 CHClF 0.91 3.86 2 1.96 HCC-140 CCl.sub.3 CH.sub.3 1.2 1.21 6.3 6.3 ______________________________________
It would be desirable to have substitutes with OH rate constants of at least about 8 cm .sup.3 /molecule/sec.times.10.sup.-14 which equates to an atmospheric lifetime of 12 months or less.
If the OH rate constant of a compound is too high, the compound is a VOC (Volatile Organic Compound) because it is so reactive that it forms carbon dioxide which contributes to global warming. Thus, it would be desirable to have substitutes with OH rate constants of 25 cm.sup.3 /molecule/sec.times.10.sup.-14 or less which equates to an atmospheric lifetime of at least 4 months.
Commonly assigned U.S. Pat. No. 4,947,881 teaches a method of cleaning using hydrochlorofluoropropanes having 2 chlorine atoms and a difluoromethylene group. European Publication 347,924 published Dec. 27, 1989 teaches hydrochlorofluoropropanes having a difluoromethylene group. International Publication Number WO 90/08814 published Aug. 9, 1990 teaches azeotropes having at least one hydrochlorofluoropropane having a difluoromethylene group.
A wide variety of consumer parts is produced on an annual basis in the United States and abroad. Many of these parts have to be cleaned during various manufacturing stages in order to remove undesirable contaminants. These parts are produced in large quantities and as a result, substantial quantities of solvents are used to clean them.
Thus, substitutes having OH rate constants between about 8 and about 25 cm.sup.3 /molecule/sec.times.10.sup.-14 and which are useful in many applications including as solvents are needed in the art.